feat(game): add ability to use a custom page model

[theEvilReaper]

Proposed changes

This pull request adds the option to use a custom item model for pages instead of the default vanilla paper item. To enable this feature, the system property cygnus.custom_pages must be set to true (e.g. via a JVM start flag: -Dcygnus.custom_pages=true). By default, this property is set to false, so custom page models are disabled unless explicitly enabled.

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

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• I have read the CONTRIBUTING.md
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[github-actions]

Test results

 99 files   99 suites   1m 0s ⏱️
 95 tests  90 ✅  5 💤 0 ❌
288 runs  273 ✅ 15 💤 0 ❌

Results for commit 7e35caa.